Velleman DCA55 - Manual (Page 21)

Atlas DCA User Guide October 2007 – Rev 7
Page 21
Thyristors (SCRs) and Triacs
Sensitive low power thyristors (Silicon Controlled
Rectifiers - SCRs) and triacs that require gate
currents and holding currents of less than 5mA
can be identified and analysed with the Atlas DCA.
Thyristor terminals are the anode,
cathode and the gate. The pinout of the
thyristor under test will be displayed on
the next press of the scroll-off button.
Triac terminals are the MT1, MT2 (MT
standing for main terminal) and gate.
MT1 is the terminal with which gate
current is referenced.
1. The unit determines that the device under test is a triac by checking
the gate trigger quadrants that the device will reliably operate in.
Thyristors operate in only one quadrant (positive gate current, positive
anode current). Triacs can typically operate in three or four quadrants,
hence their use in AC control applications.
2. The test currents used by the Atlas DCA are kept low (<5mA) to
eliminate the possibility of damage to a vast range of component
types. Some thyristors and triacs will not operate at low currents and
these types cannot be analysed with this instrument. Note also that if
only one trigger quadrant of a triac is detected then the unit will
conclude that it has found a thyristor. Please see the technical
specifications for more details.
Sensitive or low
power thyristor
RED GREEN BLUE
Gate Anod Cath
Sensitive or low
power triac
RED GREEN BLUE
MT1 MT2 Gate